1. Field of the Invention
The present invention relates to a facsimile apparatus provided with an image information send/receive function for an automatic request for repetition mode.
2. Discussion of the Background
In general, a facsimile apparatus transmits image information, the facsimile apparatus on the receive side is influenced by stochastic transmission errors that occur due to statuses in a line. An automatic request for repetition mode has been used in order to eliminate the influence of these transmission errors. In the automatic request for repetition mode, when a transmission error has been detected by a facsimile apparatus on the receive side (hereinafter termed a receiver), on the basis of the request from the receiver, a facsimile apparatus on the transmission side (hererinafter termed a transmitter) retransmits the image information.
In such an automatic request for repitition mode, the image information for transmission is divided into blocks of a predetermined data length and each block data is, for example, shaped into frames with the format indicated in FIG. 1. Then, the transmitter transmits the data in the block order indicated in FIG. 2. The frame indicated in FIG. 1 is the unit of information transfer for HDLC (High Level Data Link control procedure). This frame has a start flag (SF) comprising a predetermined bit pattern expressing the head of the frame, an address field (AF) comprising a predetermined bit pattern, a control field (CF) expressing the block order of the transmission data, a data field (DT) in which the image information for transmission is arranged in units of one block, a frame check sequence (FCS) for detecting data errors generated in the frame, and an end flag (EF) comprising a predetermined bit pattern expressing the end of the frame. In addition, in the automatic request for repetition mode, "A", "B" and "C" are used as the block order information arranged in the control field (CF).
The receiver refers to the frame check sequence (FCS) of the received frame and makes a judgment as to whether or not there are any data errors in the received frame. If it judges that a data error does not occur, the receiver sends the signal (ACK) which has a predetermined frequency expressing the normal receiving as the response. If it judges that there is a data error, then the receiver drops the level of the signal (ACK) while the next frame data is being received. This is to say that the signal (NACK) is sent as a response. (Refer to FIG. 2(b).) Then, when the signal (ACK) is received by the transmitter, the transmitter successively transmits the frame in which the data of the following frame has been set, and when the signal (NACK) is received, retransmits the block from the frame two before that frame which was received. When the receiver receives the frame for the block for which receive was expected, if that frame includes no errors, then the contents of the data field (DT) of that frame are taken as image information (Refer to FIG. 2(c) through (e).)
In this manner, when a data transmission error has occurred, the receiver notifies the transmitter to retransmit the block in which the transmission error has occurred. The transmitter then retransmits the data for the block for which the request was made. Accordingly, the receiver can obtain image information that does not contain any errors.
Now, as the signal (ACK) and the signal (NACK) which are sent from the receiver to the transmitter, a so-called backward band signal, are transmitted at such as 330 HZ for example, separated from the frequency band used by the modem functions in order to transmit the information is used.
FIG. 3 indicates the configuration of a transmission control portion of a conventional facsimile apparatus having an automatic request for repetition mode using such a backward signal. The signal from a telephone line is input to a network control device (not indicated in the figure) that connects a facsimile apparatus and a telephone line. The signal output from the network control device is received by the facsimile apparatus. The receive signal in this facsimile apparatus is supplied via a high-pass filter 1 to remove the signal component of the low-frequency band and which is included in the telephone line, to a band elimination filter 2 and a band-pass filter 3. The band elimination filter 2 removes the signal component of the frequency f.sub.1 of the backward signal from the input signals. The signal output from this band elimination filter 2 is supplied via an equalizing circuit 4 to the receive signal input terminal of a modem (not indicated in the figure). The band-pass filter 3 extracts only the signal components of the frequency of the backward signal. The signals output from this band-pass filter 3 are supplied to a backward signal detect circuit 5. The signal (SB) output from this backward signal detect circuit 5 is supplied to a controller 6 that performs the function control processing for this transmission portion. The transmission signal output from the modem is supplied to an input terminal 8a of a 3-terminal switcher 8. This transmission signal is also supplied to a band elimination filter 9 via an amplifier 7. The band elimination filter 9 removes the signal component of the frequency f.sub.1 from the input signal and the signals output from this band elimination filter 9 are supplied to an input terminal 8b of the 3-terminal switcher 8. The backward signal generation circuit 10 generates backward signals in order to respond to the transmitter in the automatic request for repetition mode. The signals from this backward signal generation circuit 10 are supplied to a band pass filter 11. The band pass filter 11 extracts the signal component of the frequency f.sub.1 from the input signals and the signal output from this band pass filter 11 is supplied to an input terminal 8c of a 3-terminal switcher 8. The signals output from a common connection terminal 8d of the 3-terminal switcher 8 is input to the band pass filter 13 via an attenuator 12. The band pass filter 13 extracts from the input signals, the signal of the frequency band in accordance with the frequency characteristics of the telephone line. The signal output from this band pass filter 13 is supplied to the input terminal of the network control apparatus connected to the telephone line. In addition, the amplifier 14 and a second call signal detect circuit 15 detect second call signals, such as tone signals of 1300 Hz for example, supplied via the telephone line and the network control apparatus to call the facsimile apparatus. The detect signal from the second call signal detect circuit 15 are supplied to a controller 6.
When transmission and receive of a transmission control procedure signal is performed in accordance with the transmission control procedures and using a low-speed modem function (CCITT V.21 modem function) of a modem, and when image information is transmitted without using an automatic request for repetition mode, the instructions from the controller 6 are used as the basis for the 3-terminal switcher 8 to switch the 25 input terminal 8a. By the 3-terminal switcher 8 selecting the input terminal 8a, the signal output from the modem is supplied to the attenuator 12 via the 3-terminal switcher 8 and the signal is adjusted to an appropriate level by the attenuator 12. The signal output from the attenuator 12 is output to the network control apparatus via a band pass filter 13 and is also output to a telephone line via the network control apparatus. In this case, the signals received via the telephone line are sent to a modem via the high-pass filter 1, the band elimination filter 2 and the equallizing circuit 4.
In the automatic request for repetition mode, when the image information is sent, the instructions from the controller 6 are used as the basis for the 3-terminal switcher 8 to switch the input terminal 8b. Accordingly, the modulated signal for the image information output from the modem is input to the band elimination filter 9 via the amplifier 7. The backward signal component in the modulated signal is removed by the band elimination filter 9. Then the output signal from the band elimination filter 9 is supplied to the network control apparatus via the 3-terminal switcher 8, the attenuator 12 and the band pass filter 13.
The controller 6 judges whether the backward signal sent from the receiver is the signal (ACK) or the signal (NACK) while monitoring the detection signal from the backward signal detect circuit 5. The results of this judgment are used as the basis for performing retransmission processing of the block data described above.
In addition, in the automatic request for repetition mode, when the image information is received, the 3-terminal switcher selects the input terminal on basis of the instruction from the controller 6. Then the backward signal generation circuit 10 generates a backward signal in accordance with the error judgment result for the frame of the received image information in order to notify of the error generation status for the received frame. This backward signal has the frequency components of other frequencies removed by the band pass filter 11. Then, the signal output from the band pass filter 11 is output to the network control apparatus via the switcher 8, the attenuator 12 and the band pass filter 13 and is then output to the telephone line via the network control apparatus.
When the backward signal is output to the transmission line of the telephone line, the backward signal appears in line due to the crosstalk. However, the component of the backward signal included in the receive signal input to the high-pass filter 1 is removed by the band elimination filter 2 and so deterioration of the receive signal by this component is prevented.
In the facsimile apparatus having a configuration such as this, the band elimination filter to remove the backward signal and the band pass filter to extract the backward signal are both provided with a transmission system and a receive system for the signals.
The band elimination filter and the band pass filter that are provided to each system are not simultaneously used. Accordingly, when both the band elimination filter and the band pass filter have been provide with these, it is both superfluous and increases the cost of the apparatus.